In recent years increasing efforts have been focussed on reducing the reliance on fossil fuels as a primary resource for the provision of fuels and commodity chemicals. Carbohydrates and related ‘biomass’ are seen as key renewable resources in the efforts to provide new fuels and alternative routes to desirable chemicals.
In particular, certain carbohydrates can be reacted with hydrogen in the presence of a catalyst system to generate polyols and sugar alcohols, such as glycols. An example of such a process is described in Angew. Chemie. Int. Ed. 2012, 51, 3249 and US 2011/0313212 and may be used to provide ethylene glycol and 1,2-propylene glycol, which are valuable materials with a multitude of commercial applications, e.g. as heat transfer media, antifreeze, and precursors to polymers, such as PET. Ethylene and 1,2-propylene glycols are traditionally made on an industrial scale by hydrolysis of the corresponding alkylene oxides, which are the oxidation products of ethylene and propylene, produced from fossil fuels.
The conversion of carbohydrates to polyols and sugar alcohols may be carried out in a batch or semi-batch process in the art. In the processes described in CN 102675045, reactants are added to the reactor and it is heated and pressurised. After the reaction is complete, the reactor is cooled and de-pressurised before the desired products can be recovered.
US 2011/0303212 describes a continuous process for generating polyols from a cellulose-containing feedstock. In this process, hydrogen, water, catalyst and co-products are all separately recovered and recycled. The recycled hydrogen requires re-pressurisation before being fed back to the reactor.
A considerable amount of energy is required by prior art processes in order to heat and pressurise the reactor and to provide suitable conditions for the conversion of saccharides into polyols. This energy is often lost or used inefficiently during product recovery.
There remains a requirement for a continuous process for the conversion of saccharides into polyols, especially glycols, in which the energy present in the reactor effluent stream is preserved and efficiently re-integrated into the process.